The present invention relates to an improved guide member for use when inserting a catheter into a vein or artery. More specifically, the present invention is directed toward an improved steerable guide member having an inner member which is rotatable with respect to a surrounding outer member over a major portion of the overall length of the guide member and is attached at its distal end to the outer member and to a formable tip member.
In recent years, many advances have been made in the catheter art and, in particular, the art associated with angioplasty catheters used in treating cardiovascular disease. However, problems have remained in the characteristics of the means employed for guiding such catheters through blood vessels.
Prior art guides are typically comprised of a tightly wound helical coil surrounding a single strand core wire where the two are welded together at the proximal and distal ends. Such guide means are advanced through an artery, for example, by first manually forming the wire at its distal tip, inserting the guide wire into the catheter, and then advancing the guide wire and catheter through the vessel while rotating its proximal end in an attempt to steer the formed distal end. However, such prior art guides have proven to be less than optimum in their design as far as the ability to transfer torque applied at the proximal end thereof to the distal tip to effect steering thereof. The physician must grasp the proximal end of the guide and attempt to rotate it as a unit, either within a blood vessel or within the lumen of a guide catheter. The substantial contact between the guide wire and the blood vessel or guide catheter presents frictional forces which must be overcome. As a result, the movement of the formed distal end portion of the guide wire tends to be somewhat erratic and unpredictable. Moreover, the contour of the wound coils results in a guide wire having a rough surface which is inclined to be more thrombogenic than a smooth surface.
Another type of guide which has been used is a polymer coated wire strand. Applying a torque to its proximal end causes the entire wire to rotate. However, this design is considered to be less advantageous because the tip cannot be bent or formed. Further, the coefficient of friction between this guide and the vascular wall surfaces makes the guide difficult to rotate and steer through the blood vessel.
A third catheter guide design which has gained some attention incorporates a core wire coated with a polymer which terminates approximately five inches from the guide's distal tip. A tightly wound helical coil covers the last five inches or so of the core wire. This design, however, still suffers from the problem that torque can only be transferred to the tip by rotating the entire guide wire thus increasing friction. Further, the flexibility of the shaft cannot readily be varied in this design.